Artificial spinal fusion implants

ABSTRACT

A spinal implant is disclosed which when placed within the spinal disc space stabilizes that spinal segment and materially participates in, and is incorporated in, the ensuing fusion.

BACKGROUND

[0001] The present invention relates to an artificial fusion implant tobe placed into the intervertebral space left after the removal of adamaged spinal disc.

[0002] The purpose of the present invention is to provide an implant tobe placed within the intervertebral disc space and provide for thepermanent elimination of all motion at that location. To do so, thedevice is space occupying within the disc space, rigid, self-stabilizingto resist dislodgement, stabilizing to the adjacent spinal vertebrae toeliminate local motion, and able to intrinsically participate in avertebra to vertebra bony fusion so as to assure the permanency of theresult.

[0003] At present, following the removal of a damaged disc, either boneor nothing is placed into the space left. If nothing is placed in thespace the space may collapse which may result in damage to the nerves;or the space may fill with scar tissue and eventually lead to areherniation. The use of bone is less than optimal in that the boneobtained from the patient requires additional surgery and is of limitedavailability in its most useful form, and if obtained elsewhere, lacksliving bone cells, carries a significant risk of infection, and is alsolimited in supply as it is usually obtained elsewhere, lacks living bonecells, carries a significant risk of infection, and is also limited insupply as it is usually obtained from young accident victims.Furthermore, regardless of the source of the bone, it is only marginalstructurally and lacks a means to either stabilize itself, againstdislodgement, or to stabilize the adjacent vertebrae.

[0004] A review of all possibly related prior art will demonstrate thenovelty of the present invention.

[0005] There have been an extensive number of attempts to develop anacceptable disc prothesis (an artificial disc). Such devices by designwould be used to replace a damaged disc and seek to restore the heightof the interspace and to restore the normal motion of that spinal joint.No such device has been found that is medically acceptable. This groupof prosthetic or artificial disc replacements seeking to preserve spinalmotion which are different from the present invention include:

[0006] U.S. Pat. No. 3,867,728 STUBSTAD—describing a flexible discimplant.

[0007] U.S. Pat. No. 4,349,921 KUNTZ—describing a flexible discreplacement with rope or file like surface projections to discouragedevice dislocation.

[0008] U.S. Pat. No. 4,309,777 PATIL—describing motion preservingimplant with spike outer surfaces to resist dislocation and containing aseries of springs to urge the vertebrae away from each other.

[0009] U.S. Pat. No. 3,875,595 FRONING—describing a motion preservingbladder like disc replacement with two opposed stud like projections toresist dislocation.

[0010] U.S. Pat. No. 2,372,622 FRENCH (FASSIO)—describing a motionpreserving implant comprising complimentary opposed convex and concavesurfaces.

[0011] In summary then, these and other similar devices resemble thepresent invention only in that they are placed within the intervertebralspace following the removal of a damaged disc. In that they seek topreserve spinal motion, they are diametrically different from thepresent invention which seeks to permanently eliminate all motion atthat spinal segment.

[0012] A second related area of prior art includes those devicesutilized to replace essentially wholly removed vertebrae. Such removalis generally necessitated by extensive vertebral fractures, or tumors,and is not associated with the treatment of disc disease, or thereforerelated to the present invention. While the present invention is to beplaced within the disc space, these prior devices cannot be placedwithin the disc space as at least one vertebrae has already been removedand there no longer remains a “disc space.” Furthermore, all of thesedevices are limited in that they seek to perform as temporary structuralmembers mechanically replacing the removed vertebrae (not a removeddisc), and do not intrinsically participate in supplying osteogenicmaterial to achieve cross vertebrae bony fusion. Therefore, again unlikethe present invention which provides for a source of osteogenesis, useof this group of devices must be accompanied by a further surgeryconsisting of a bone fusion procedure utilizing conventional technique.This group consisting of vertebral struts rather than disc replacementswould include the following:

[0013] U.S. Pat. No. 4,553,273 WU—describing a turnbuckle like vertebralstrut.

[0014] U.S. Pat. No. 4,401,112 REZAIAN—describing a turnbuckle likevertebral strut with the addition of a long stabilizing staple thatspans the missing vertebral body.

[0015] U.S. Pat. No. 4,554,914 KAPP—describing a large distractiblespike that elongates with a screw mechanism to span the gap left by theremoval of a entire vertebrae and to serve as an anchor for acryliccement which is then used to replace the missing bone (vertebrae).

[0016] U.S. Pat. No. 4,636,217 OGILVIE—describing a vertebral strutmechanism that can be implanted after at least one vertebrae has beenremoved and which device consists of a mechanism for causing theengagement of screws into the vertebrae above the vertebrae below theone removed.

[0017] In summary then, this group of devices differs from the presentinvention in that they are vertebral replacements struts, do notintrinsically participate in the bony fusion, can only be inserted inthe limited circumstances where an entire vertebrae has been removedfrom the anterior approach, and are not designed for, or intended to beused for the treatment of disc disease.

[0018] A third area of prior art related to the present inventionincludes all devices designed to be applied to one of the surfaces ofthe spine. Such devices include all types of plates, struts, and rodswhich are attached by hooks, wires, and screws. These devices differsignificantly from the present invention in that they are not insertedwithin the disc space, and furthermore do not intrinsically participatein supplying osteogenic material for the fusion.

[0019] Therefore, with these devices where permanent spinalimmobilization is desired an additional surgery consisting of a spinalfusion performed by conventional means or the use of supplementalmethylmethacrylate cement is required. Such devices, applied to thespine but not within the disc space, would include the following:

[0020] U.S. Pat. No. 4,604,995—STEPHENS—describing a “U” shaped metalrod attached to the posterior elements of the spine with wires tostabilize the spine over a large number of segments.

[0021] U.S. Pat. No. 2,677,369—KNOWLES—describing a metal column deviceto be placed posteriorly along the lumbar spine to be held in positionby its shape alone and to block pressure across the posterior portionsof the spinal column by locking the spine in full flexion therebyshifting the maximum weight back onto the patient's own disc.

[0022] Other devices are simply variations on the use of rods (e.g.Harrington, Luque, Cotrel-Dubosset, Zielle), wires or cables (Dwyer),plates and screws (Steffee), or struts (Dunn, Knowles).

[0023] In summary, none of these devices are designed for or can be usedwithin the disc space, do not replace a damaged disc, and do notintrinsically participate in the generation of a bony fusion.

[0024] Other prior art possibly related to the present invention andtherefore, to be considered related to “Bony Ingrowth”. Patents relatedto this feature describe either methods of producing materials ordevices to achieve the same. Such patents would include:

[0025] U.S. Pat. Nos. 4,636,526 (DORMAN), No. 4,634,720 (DORMAN), No.4,542,539 (ROWE), No. 4,405,319 (COSENTINO), No. 4,439,152 (SMALL), No.4,168,326 (BROEMER), No. 4,535,485 (ASHMAN), No. 3,987,499 (SCHARBACH),No. 3,605,123 (HAHN),No. 4,655,777 (DUNN), No. 4,645,503 (LIN), No.4,547,390 (ASHMAN), No. 4,608,052 (VAN KAMPEN), No. 4,698,375 (DORMAN),No. 4,661,536 (DORMAN), No. 3,952,334 (BOKROS), No. 3,905,047 (LONG),No. 4,693,721 (DUCHEYNE), No. 4,070,514 (ENTHERLY).

[0026] However, while the present invention would utilize bone ingrowthtechnology, it would do so with conventional technology.

[0027] The final area of related prior art to be considered is that ofdevices designed to be placed within the vertebral interspace followingthe removal of a damaged disc, and seeking to eliminate further motionat that location.

[0028] Such a device is contained in U.S. Pat. No. 4,501,269 BAGBYdescribing an implantable device, limited instrumentation, and a method;whereby a hole is bored transversely across the joint and then a hollowmetal basket of larger diameter is then pounded into the hole and thenfilled with the bone debris generated by the drilling. The presentinvention differs from the prior art devices in the following ways:

[0029] 1. UNIVERSAL APPLICABILITY WITHOUT CONTOURING OF THE INTERSPACE.The present device will fit any patient, anywhere throughout the spine,in any intervertebral disc space, and without alteration of thatinterspace regardless of its natural size or shape.

[0030] 2. RESTORATION AND PRESERVATION OF THE INTERSPACE. The presentinvention will restore the intervertebral space to its premorbiddimensions, and do so by having the implant fit the space rather thanhaving to modify the interspace, by bone removal from the vertebrae, toaccommodate the implant.

[0031] 3. END PLATE PRESERVATION. Preservation of the highly specializedweight bearing cortical bone is allowed and end plate perforation intothe highly vascular cancellous bone marrow with its attendant bleedingis avoided. Such bleeding, when it occurs, bears all the risks of bloodloss (e.g. hypoglycemic shock, transfusion transmitted diseases such ashepatitis and acquired immune deficiency syndrome, etc.), and all thecomplications arising from the resultant impaired visualization of thevital structures (e.g. nerves, blood vessels, and organs) due to suchbleeding.

[0032] 4. TECHNIQUE. The technique for insertion of these implants isconsistent with the established methods of disc removal, and requiresneither specialized instrumentation nor specialized surgical technique.

[0033] 5 EXTENT OF DISC REMOVAL. The extent of disc removal can bedetermined by the surgeon at the time surgery and can be individualizedfor each patient.

[0034] 6. NO DRILLING. No drilling is involved with the use of thepresent invention.

[0035] 7. ELIMINATION OF INCORRECT IMPLANT SIZE SELECTION. In thoseimplant systems where a drill is used and significant bone is removedthen an estimate of the implant size must first be made, and then,regardless of the fit, an implant at least as large as the space createdby the drilling must be utilized, regardless of the quality of that fit.With the present invention no significant bone is removed, and thecorrect size implants are fitted directly to the interspace eliminatingthe need to guess at the correct implant size before the fact.

[0036] 8. MODULAR DESIGN. The present implants are available in varyinglengths to accommodate the changing depths of the interspace fromcentral to lateral. The devices are available in varying heights or areinfinitely adjustable as to the height within the physiological range.The widths are standardized, and the various embodiments can be used inany combination (e.g. in the lumbar spine two auto-expanding implantscould be used in conjunction with two anchor deploying implants tocompletely fill the interspace).

[0037] 9. AVOIDANCE OF SIZE LIMITATIONS. Because in one embodiment thesystem is modular, component parts can be inserted through a very smallopening until a much larger implant is reconstituted completely fillingthe available interspace; and yet much larger when assembled than theopening through which the component modular sections were introduced.For example, in the lumbar spine four implants introduced one at a timeand measuring 8 mm in width, would when reconstituted within theinterspace constitute a 32 mm wide implant. Implantation of a singleimplant of those dimensions from a posterior approach in the lumbarspine would otherwise be impossible because of the presence of the duralsac and spinal nerves.

[0038] 10. THE AVOIDANCE OF INTERSPACE COLLAPSE. The device is manytimes stronger than bone and will not collapse. The implantation of thedevice allows preservation of the very strong vertebral cortex, which isresistant to compression preventing the migration of the implant intothe vertebrae. The large surface area of the assembled modular implant,minimizes the load per unit area. For example, a reconstituted lumbarimplant of four modular components would have the weight distributedover approximately 8 sq. cm. per vertebral interface.

[0039] 11. REMOVABILITY. Because the present invention is an interspaceimplant and not a “through vertebrae” cross interspace implant, removalof the implant, should that become necessary, would not result iniatrogenic destruction of the adjacent vertebrae.

[0040] 12. SELF-STABILIZING. The implant is self-stabilizing without theuse of threads. All of the implants are surface configured to resistdislodgement and the preferred embodiments contain active, mechanicalmeans to assure permanent anchoring. Long term stability begins with theabove and is further enhanced by surface treating of the implant forbone ingrowth (by known conventional means) and osteogenically loadingthe implants.

[0041] 13. SPINE REDUCING. Various embodiments of the present inventionsuch as the ones with the 180 degree opposed ratcheted surface, and theauto-expanding type, are capable of reducing a vertebral listheses (aforward or backward translation of one vertebrae upon another).

[0042] 14. SPINAL STABILITY. These implants are capable of stabilizing aspinal segment following disc removal, and do so without the use ofthreads (threads would be design need to violate the vertebraethemselves extensively).

[0043] 15. SAFETY. The entire procedure is performed under direct visionand with complete visualization of the adjacent vital structures (e.g.organs, neural structures and blood vessels).

[0044] In summary then, the present invention is an interspace implantutilized to replace a damaged disc, which unlike an artificial disc,seeks to permanently eliminate rather than to preserve spinal motion,and to do so by a bony fusion. The present invention is clearly animprovement over the prior art providing an interspace implantintrinsically participating in the fusion process, self-stabilizing,stabilizing to the spinal segment, consistent with conventional methodsof discectomy, and uniquely consistent with the preservation of theintegrity of the adjacent vertebrae.

BRIEF SUMMARY OF THE PRESENT INVENTION

[0045] The present invention comprises an artificial implant, thepurpose of which is to participate in, and directly cause bone fusionacross an intervertebral space following the excision of a damaged disc.Said implants are structurally load bearing devices, stronger than bone,capable of withstanding the substantial forces generated within thespinal interspace. Such devices have a plurality of macro sized cellsand openings of 1-3 mm, which can be loaded with fusion promotingmaterials, such as autogenous bone, for the purpose of materiallyinfluencing the adjacent vertebrae to perform a bony bond to theimplants and to each other. The implant casing may be surface texturedor otherwise treated by any of a number of known technologies to achievea “bone ingrowth surface” to further enhance the stability of theimplant and to expedite the fusion. Further, said devices are soconfigured and designed so as to promote their own stability within thevertebral interspace to resist dislodgement, and furthermore, tostabilize the adjacent vertebrae.

[0046] To use the implant of the present invention a conventionaldiscectomy is performed and the vertebral endplates scraped, but notperforated. The appropriately sized implants are loaded with autogenousbone and implanted within the interspace.

[0047] For example for an anterior cervical device implantation, a shorttransverse incision is made across the front of the neck and to theright of the midline directly over the diseased disc. The platysmamuscle is split, and the sternocleidomastoid muscle with is split, andthe sternocleidomastoid muscle with the carotid sheath is protected andretracted laterally. The esophagus, trachea and associated midlinestructures are protected and retracted medically, thus exposing theanterior aspect of the cervical spine. The diseased disc is identifiedand removed by conventional surgical methods. The adjacent vertebralendplates are gently scraped free of any remaining cartilage untildiffuse fine punctuate decortication is achieved. The dimensions of theinterspace are then measured in mild distraction, and the appropriateimplant selected. Cancellous bone, obtained from the patient's iliaccrest or the equivalent, is loaded into the implant. The safety driveris then utilized to insert the implant behind the anterior lips of thevertebrae. The wound is then closed in the routine manner.

OBJECTS OF THE PRESENT INVENTION

[0048] It is an object of the present invention to provide for a meansof achieving interspace fusion and stabilization as a single procedureby a means consistent with the conventional method of discectomy.

[0049] It is another object of the present invention to provide for ameans of achieving an interspace fusion and stabilization that isquicker, safer, and entails less blood loss than by any other knownmeans.

[0050] It is another object of the present invention to provide for ameans of achieving a one stage interspace fusion and stabilizationwithout significant violation or removal of the adjacent vertebral bonestock.

[0051] It is another object of the present invention to provide for amethod of intervertebral arthrodesis and stabilization of enhancedsafety where the entire procedure is performed under direct vision.

[0052] It is another object of the present invention to provide for amethod of intervertebral arthrodesis and stabilization of greatersimplicity and requiring minimal specialized instrumentation ortechnique not already possessed by those doing such procedures byconventional means.

[0053] It is another object of the present invention to provide for amodular prosthesis, allowing complimentary subunits to be insertedindividually through a small opening and to then be reassembled withinthe interspace, so as to reconstitute an interspace occupying devicemuch larger than would be insertable as a whole.

[0054] It is another object of the present invention to provide for amodular implant system such that it is possible to precisely fit thecontours of any interspace without the need to sacrifice any vertebralbone to accommodate the prosthesis. These and other objects of thepresent invention will be apparent from review of the followingspecifications and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0055]FIG. 1 is a top right perspective view of the implant (cervicaltype).

[0056]FIG. 1a is a front view of the implant of FIG. 1FIG. 1b is a rearview of the implant of FIG. 1.

[0057]FIG. 1c is a top view of the implant of FIG. 1.

[0058]FIG. 1d is a side view of the implant of FIG. 1.

[0059]FIG. 1e is a bottom view of the implant of FIG. 1.

[0060]FIG. 2 is a side sectional view of the implant viewed along lines2-2 of FIG. 1d.

[0061]FIG. 3 is the implant FIG. 1 showing the attachment to the driverand driver.

[0062]FIG. 4 is a front perspective view showing the implant beingdriven into the disc space.

[0063]FIG. 4a is a front perspective view of the implant located in thespine.

[0064]FIG. 5 is a side view of the implant in the spine attached to thedriver.

[0065]FIG. 5a is a close up partial sectional view of the implant anddriver.

[0066]FIG. 6 is a perspective view of a series of implants placed in thecervical intervertebral space.

[0067]FIG. 6A is an alternative embodiment of a rectangular solidimplant.

[0068]FIG. 7 is a side sectional view of the vertebrae and implantviewed along lines 7-7 of FIG. 6.

[0069]FIG. 7A is a side sectional view of the vertebrae structureshowing a third embodiment of the rectangular solid implant in place.

[0070]FIG. 8 is an exploded perspective view of another embodiment ofthe present invention.

[0071]FIG. 9 is a side sectional view of the vertebrae structure andimplant viewed along lines 9-9 of FIG. 8.

[0072]FIG. 10 is a side sectional view of the implant of FIG. 8, in acontracted position.

[0073]FIG. 11 is a side sectional view of the implant of FIG. 10, in anexpanded position.

[0074]FIG. 12 is a perspective view of an alternative embodiment of theimplant of FIG. 9.

[0075]FIG. 13 is an alternative embodiment of a hollow rectangular solidimplant.

[0076]FIG. 14 is a cross sectional view of the hollow rectangular solidimplant of FIG. 13 viewed along lines 14-14 of FIG. 13.

[0077]FIG. 15 is an alternative embodiment of an expandable implant inits extended position.

[0078]FIG. 16 is an expandable implant of FIG. 15 in its retractedposition.

[0079]FIG. 17 is an expandable implant of FIG. 16 located in the discspace.

[0080] Referring to FIGS. 1 through 5 an implant for use in the discspace and associated apparatus used for inserting the implant 10 isshown. The implant 10 is shown as a substantially rectangular hollowconfiguration, having a tapered forward portion.

[0081] The implant 10 has an upper surface 12 and a parallel lowersurface 14. The two side walls 16 and 18 are parallel to one another andhave a series of small sized openings 20 of 1 mm-3 mm through the sidewalls 16 and 18.

[0082] The front wall 22 is slightly convex and has a depressed portion24 with a central threaded opening 26 for receiving the engaging end 28of a driving member 30.

[0083] The upper surface 12 has a threaded cap 32, which has opening 33there through, with a central allen wrench opening 34 for engagementwith an allen wrench A of FIG. 3. The cap 32 covers the opening into thehollow implant 10 and permits the insertion of autogenous bone materialinto the hollow portion of the implant 10. The cap 32 is surrounded by aseries of small sized openings 36 of 1 mm to 3 mm passing through theupper surface and into the central hollow portion of the implant 10.

[0084] The rear wall 38 is convex so as to conform to the rear of thedisc space.

[0085] The driving member 30, shown in FIG. 3, comprises a substantiallyhollow tubular member 40 having a long internal rod 42 having a turningknob 44 at one end and a threaded portion 46 at the other end forthreadably engaging the threaded opening 26 of the implant 10. Theengaging end 28 of the driving member 30 has a slightly convex surfaceto complement the slightly convex surface of the front wall 22. Theengaging end 28 has an extension 48 for fitting within the depressedportion 24 on the front wall 22 of the implant 10. The engaging end 28also has restriction members 47 and 49 to restrict the depth ofpenetration of the driver 30.

[0086] In use, the cap 32 is removed from the implant 10 and autogenousbone material is inserted into the hollow portion of the implant 10. Thecap is then replaced. Various methods of packing the implant 10 with theautogenous bone material may be used to obtain a completely packedimplant 10.

[0087] Referring to FIGS. 4, 4a, 5 and 5 a, the method of inserting theimplant is shown. The threaded end 46 of the internal rod 42 of thedriving member 30 is attached to the threaded opening 26 of the implant10 by turning of the knob 44. Once the engaging end 28 is in place, thefitting of the extended portion 48 into the depressed portion 24prevents movement of the implant 10 in relationship to the drivingmember 30.

[0088] The implant is then placed at the entrance to the disc spacebetween the two adjacent vertebrae V. The knob 44 is then tapped withhammer H sufficiently hard enough to drive the implant 10 into the discspace. The restriction members 47 and 49 which are wider than the discspace, prevent over penetration of the implant.

[0089] The size of the implant 10 is substantially the same size as thedisc space that it is replacing and thus will be larger or smallerdepending on the disc space in which it is to be used. In the preferredembodiment the implant 10 is approximately 32 mm wide.

[0090] Referring to FIGS. 4A and 5 the implant 10 is shown in place inthe disc space after removal of the driving member once the implant wasinserted in place.

[0091] The autogenous bone material that was packed within the hollowportion of the implant 10 serves to promote bone ingrowth between theimplant and the adjacent vertebrae. Once the bone ingrowth occurs, theimplant 10 will be a permanent fixture preventing dislodgement of theimplant as well as preventing any movement between the adjacentvertebrae.

[0092] Referring to FIG. 6 an alternative embodiment of the implant isdisclosed. The implant 61 comprises a substantially rectangular memberhaving a series of ridges 62 on the upper and lower surfaces of theimplant 60. One or more grooves 64 are placed on the upper and lowersurfaces as well. As indicated in FIG. 6, a series of such implants 61are used as the interbody spinal implant, each placed closely adjacentone another to approximate the size of the removed disc. A series ofmicro sized openings 63 perforate the implant 61, to promote boneingrowth.

[0093] The implant of FIG. 6 is inserted as follows: the disc issubstantially removed by conventional means. The implants 61 are theninserted in the intervertebral space between the two vertebrae.

[0094] The size of the implant 61 of FIG. 6 is approximately 26millimeters in length and is wide enough so that four of them willsubstantially fill the intervertebral space, depending on whichvertebras are fused.

[0095] In FIG. 6a a “bullet nosed” implant 67 having a open frontportion 69 to facilitate insertion of implant 67 is shown.

[0096] Referring to FIGS. 7 and 7a alternative embodiments of theimplant 61 of FIG. 6 is shown in place between two vertebrae V.

[0097] In FIG. 7 the implant 70 is shown with the ridges 62 shown in theform of teeth facing the anterior. These ridges serve to prevent theimplant 60 from ‘walking’ out of the space between the vertebrae.

[0098] In FIG. 7a an embodiment of the implant 70 of FIG. 6 is shownhaving opposed ridges 72 and 74. This serves to maintain the alignmentof the vertebrae when the two vertebrae V are improperly aligned withrespect to one another.

[0099] Referring to FIG. 8 an adjustable implant 8 i having means foradjusting the width of the implant 81 is shown. The implant 81 comprisesa lower member 82 and an upper member 84 which when fitted together forman essentially rectangular implant. The upper member 84 and the lowermember 82 have hollow portions that face one another and receive taperedwedges 86 and 88 that fit within the hollow portion of the upper andlower members 82 and 84. The wedges 82 and 84 are such that at theirlarge and they are higher than the combined hollow space between theupper and lower members 84 and 82, and shallower at the other end thanthe hollow space between the upper and lower members.

[0100] The wedges 86 and 88 have a central threaded opening 90 and 92 inalignment with each other for receiving threaded screw 94. Deformableburrs 95 on the head 9B of the screw 94 are used for locking the screwin place. The implant has a series of holes 100 throughout the body ofthe implant to assist in the ingrowth process.

[0101] Referring to FIGS. 9 through 11 the expandable implant 81 isshown positioned between the two vertebrae V. In FIG. 10 the expandableimplant 81 is illustrated in its contracted position. The wedges 86 and88 abutt the interior sloped surfaces 104 of the upper and lower members82 and 84.

[0102] As the screw 94 is turned, as shown in FIG. 11, the wedges 86 and88 are drawn together, and the sloped portions of the wedges force theupper member 82 away from the lower member 84. Once the screw 94 hasbeen turned sufficiently, the screw head 98 is hit, causing thedeformable burrs to be crimped so as to prevent the reverse rotation ofthe screw 94.

[0103] In FIG. 12, another alternative embodiment of the expandableimplant 81 is illustrated with spike projections 106 extending from thetop and bottom members to dig into the vertebrae and assist inmaintaining it in place.

[0104] In use, the disc is removed, and the implant 81 is placed betweenthe vertebrae. The screw 94 is then turned expanding the implant. In thepreferred embodiment, the width is from 8 millimeters to 18 millimeters.

[0105] Referring to FIGS. 13 and 14, another alternative embodiment ofthe invention is shown in which the implant 200 comprises a rectangularhollow member having a slightly tapered forward section 202. The crosssection, shown in FIG. 14, shows the rectangular configuration of theimplant.

[0106] In use of the implant the interior of the implant is filled witha paste made of autogenous bone, and inserted in the place of the formerdisc. The strength of the material used to make the implant is suchthat, even though it is substantially hollow, it does have sufficientstrength to withstand the forces of the vertebrae compressing theimplant.

[0107] Referring to FIGS. 15-17, another alternative embodiment is shownin which the implant has movable projections which are movable from afirst position within the implant to a second position extending outsideof the implant.

[0108] The implant 300 is of a generally rectangular configuration. Thetop surface 302 and the bottom surface 304 of the implant have slots 306for permitting pivotal member 307 having spikes 308 at their ends toproject through said slots 306. The spikes 308 are pinned at one end 310within the implant 300.

[0109] Opposing wedge shaped members 312 and 314 having a centralthreaded opening 316 for receiving a threaded screw 318 having a head320 and a slot 322. The wedges are facing each other so that uponturning of the screw will draw the two wedges together, causing thewedges to cause the spikes 308 to pivot about their end 310 and causethe spikes to project out of the implant through the aligned slots 306.The depressions 329 in the pivotal member 307 engage the wedges 314 and312 to lock the pivotal members 307 in place. A series of holes 324 forpromoting bone ingrowth and fusion are provided in the implant 300.

[0110] In use, after the removal of the disc material, the implants withthe spikes 308 in their withdrawn position, are inserted into the discspace. Then the screw 318 is turned until the spikes 308 are forced toenter the vertebrae material, as shown in FIG. 17. The implant 300 isthus held firmly in place.

[0111] These implants have a surface configuration so as to induce boneingrowth through the implant, and into the wall of the vertebrae ineffect inducing fusion from one vertebrae V joint to the other, therebyeventually making the implant itself superfluous as the bone would dothe work.

[0112] The implant itself, because of its being made of strongermaterial than bone, would provide structural support to the twovertebrae while awaiting bone ingrowth. Once the bone ingrowth occurred,however, the implant would be firmly and permanently fixed in place.

[0113] While the invention has been described with regards to thepreferred embodiment and a number of alternative embodiments, it isrecognized that other embodiments of the present invention may bedevised which would not depart from the scope of the present invention.

What is claimed is:
 1. An implant for fusion of two adjacent vertebraein the spine said implant comprising a generally rectangular member,said member having a plurality of openings therein for promoting boneingrowth with the implant and fusion of said vertebrae.
 2. The implantof claim 1 in which said rectangular member has a plurality of ratchetlike members facing in the same direction on the upper and lowersurfaces of said member for engagement with adjacent vertebrae.
 3. Theimplant of claim 2 in which said ratchet like members on the upper andlower faces face in different directions to prevent movement of theadjacent vertebrae relative to each other.
 4. The implant of claim 1 inwhich said implant has a tapered portion at one end.
 5. The implant ofclaim 1 in which the rectangular member is separable into an upperportion and a lower portion, and comprises a wedge means fitted betweensaid upper portion and said lower portion for forcing said upper portionaway from said lower portion.
 6. The implant of claim 5 in which saidwedge means comprises a central threaded opening with a threaded screwconnecting two of said wedges, whereby turning said threaded screw drawssaid wedges together and forces said upper portion and lower portion ofsaid implant away from each other.
 7. The implant of claim 6 in whichsaid implant has a plurality of openings therethrough.
 8. The implant ofclaim 6 in which said upper and lower surface of said implant hasprojections for engaging the vertebrae.
 9. The implant of claim 1 inwhich said implant has a plurality of slots in the upper and lowersurfaces and a plurality of pivotal members movable between-a firstposition within said implant and a second position outside of saidimplant through said slots.
 10. A spinal implant comprising a hollowrectangular member, said rectangular member having a removable cap forcovering said opening.
 11. The implant of claim 10 in which said implanthas a plurality of openings through the walls of said implant.
 12. Theimplant of claim 10 in which said implant is substantially the sameshape and dimensions as a disc.
 13. The implant of claim 10 in whichsaid implant comprises a front surface having an threaded openingtherein for engagement with a threaded driving member.
 14. The implantof claim 13 in which said front surface has a driver engaging portion.15. The implant of claim 14 in which said engaging means comprises adepression on the front surface
 16. The implant of claim 10 in whichsaid removable cap includes threads for attachment to said implant. 17.A driving member for driving a spinal implant comprising a first hollowtubular member, said hollow member having an irregular end forconfirming to the external shape of a front surface of a spinal implant,and a second rod member fitted within said hollow tubular member saidrod member having a threaded portion at one end and an enlarged knobportion at the other end.
 18. The driver member of claim 17 in whichsaid irregular end comprises an extended portion for fitting within adepressed portion of a spinal implant.
 19. A spinal implant comprising agenerally rectangular ember having a dimension of less than the width ofa disc space, whereby a plurality of said implants of different widthshave a width of the size of a disc space.
 20. A plurality of spinalimplants, the combined width of said spinal implants approximating thewidth of the disc space.
 21. A method for replacing a disc in the spinecomprising removing the disc and inserting into the resulting disc spacea plurality of implants having a combined width approximating the widthof the disc space.
 22. The method of claim 21 in which said implants areinserted into the disc space one at a time.
 23. The method of claim 21in which said implant is made of a material that promotes bone ingrowth.24. The method of claim 21 including the step of inserting autogenousbone material within said implant before implanting.